Comparing outdoor sound propagation simulations based on geometrical and numerical methods

Conventional simulations of outdoor noise propagation often rely on geometrical acoustic methods such as ray tracing or mirror sources. Especially for low frequencies, these methods deliver physically implausible results due to their inherent approach not resolving the properties of the acoustic field. In this contribution, the results of a conventional noise propagation simulation software based on geometrical acoustics are compared to numerical results originating from solving the Helmholtz equation with the Finite Element Method (FEM). A 2.6 km long cross-section through an alpine valley with a railway line is considered as an exemple. In comparison with the FEM results, the shortcomings of geometrical acoustic methods are demonstrated, which underline the need for powerful and computationally efficient numerical approaches for outdoor noise propagation.